Electrical testing system



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S. l. GORY ELECTRICAL TESTING SYSTEM Filed July 16. 1921 www @SSE

t. ATTORNEY Patented ct. lll, 1924.

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SAMUEL I. CORY, OF ELMHURST, NEW YORK, ASSIGNOR TO AMERICAN TELEPHONEAND TELEGRAPH GO'MPANY, A CORPORATION 0F NEV YORK.

ELEC'lldflCAL` TESTING SYSTEM.

Application mea July 1c, 1921.

To alt ifa/2,0m t may concern.'

Be it known that l, SAMUEL I. CORY, residing at Elmhurst, in Ithe countyof Queens and State of New York, have invented certain Improvements inElectrical Testing Systems, of which the following is a speciication. Y

This invention relates to electrical testing systems and particularly toan arrangement for determining the degree of unbalance between twonetworks, such as a signaling circuit and the network designed tobalance the said circuit.

Inorder to operate miost efficiently certain types of signalingcircuits, as, for eX- amp-le telephone repeater circuits and duplextelegraph circuits, it is necessary to maintain a high degree of balancebetween the 'line circuit` and the network which is intended to balancethe said circuit.

To attain this result, it is necessary to determine the degree ofunbalance between a line circuit and its balancing network. Anarrangement for determining the unbal ance between a line and itsnetwork in a telephone repeater circuit is shown in the application ofClark and Crisson, Serial No. 395,365, filed July 10, 1920; lThisprovides for the determination of the degree of unbalance by applyingsinusoidal waves of different frequencies, preferably throughout thevoice range, and determining the unbale ance at each frequency. Such amethod of measuring is desirable in telephony because we are thereconcerned with the steady-'state condition, but in telegraphy thetransient phenomena are-of greater concern.

A telegraph signaling impulse is a steep sloped wave comprising aplurality of different frequencies which are simultaneously impressedupon the line circuit whenever the key of the transmitting device isclosed. It will accordingly be seen that in telegraphy the transientphenomena are of prime importance, and consequently, a measurement madeby a sinusoidal wave of a definite frequency does not give correctresults.

It is well known to those familiar with the art, of duplex telegraphythat if unbalance exists between a line circuit and a network which isdesigned to simulate electrically the said circuit, the application ofsignaling impulses to; the line circuit by the transmitter connected,with the terminal Si?? serial No. 485,206.

cuit at one end of the said line circuit will cause the receivingrelayconnected with the same terminal circuit to respond to thetransmitted signals, the degree of response depending upon the amount ofunbalance existing between the line circuit and its balancing network.This reaction of the transmitted signals upon the receiving relay, dueto imbalance between the line and its network, causes distortion of thetelegraph sig nails received from the distant transmitting circuit, thedistortion manifesting itself in lengthening or shortening the receivedsignal impulses.

In the copending application of Nyquist, Serial No. 485,308, iiled July16, 1921, there was disclosed means for measuring duplex imbalance whichembodied the use of adistortionbridge circuit connected with thereceiving circuit in which the unbalance was to be measured. `In theapplicants system, the magnitude of the unha-lance is determined bymeans of a milliammeter connected with the receiving circuit, whichresponds either to the resultant current of two waves impressed upon thereceiving circuit in the manner disclosed in the Nyquist application. oras the result of the application of signaling impulses by thetransmitter circuit connected with the terminal circuit where theunbalance is being measured, which method will be made clear in th-efollowing description of the invention.

Although this invention will be described in connection with a metallicduplex telegraph circuit it is to be understood that it is not limitedto this particular type of circuit but is capable of'measuringunbala-nces existing between any two types of networks.

This invention will be better understood from the following descriptionwhen read in connection with the attached drawing of which Figure 1shows one form of embodiment ofthe invention and Fig. 2 shows currentcurves 2, 2", 2 and 2d, which serve to make clear the principle involvedin this invention.

In Fig. 1, a line circuit L extends between two stations X and Y.Connected with the lin-e L at the station X is a balancing hav-ing aplurality of windings designated 1, 2, 3, 4, and 6; ,Windings 1, 2, 3and 4 are of they same magnitude and are connected serially in the line.Windings 5 and 6 are connected in series with what is commonly knownl asthe vibratory circuit. All of these' windings aretarianged` upon thesame core, the magneto motive force of which is adapted to control theaction l,of the arma-v,

ture 7. v

' Brid ed across the `unction oint of windings 1 and 2, and the junctionpoint of windings 3 and 4 is the transmitting circuit 8, by

means of which signaling impulses from the `transmitter Tl areeffectively applied to the yline L fortransmission to the receivingcircuitl at the distantstation Y. This transmitl,ting circuity comprisesin addition to the Vtransmitter Tla transmitter-branch filter F,

whichisadapted to modify the kimpulses generated by the transmitter T1.so that they will have a wave shape which is best adapted vto produce anarrival wave of the most desirableform at station Y, and aty the' sametime toV prevent .interference with .the telephone signaling currentswhich might be transmitted` simultaneously over the circuit L.

f It will `be clearly seen that the current iinpressed. by thetransmitting,circuit`8 will fiow in opposite directions in windings land n 2, and also oppositel m `windings 3 and 4,

andifthe network i 1 exactly balances the line-L, thecurrent will,likewise be lof the same magnitude iin the respective windings so thatno resultant fiuX will be set up inthe core and consequently'iio'effectwill be proreduce the imbalance by pro-per adjustment.

' The vibratory circuit, in which the wind'- ings 5 and 6 are located,also contains a condenser 9 and a resistance l10, 4thefunction offwliichvwill later be made clear in the derscription of the-operationof-the circuit.

The armature7, which is connected with the i receiving circuit is,vadapted to move between thecontacts 11V and 12v with which areconnectedbatteries 13 and 14 of opposite polarity.. .Connected betweenthe batteries 13 and 14 are the resistances 15 and 16, the junctionpoint of which is connected with the junction point of the windings 5and 6. The

armature 7 is connected with amilliammeter which is in series with apolar, sounder and a resistance which is connected with the vitheresistance1'0..l. Y y, n i The ter'nina'lj circuit, at station Y is inbratory circuit between the condenser 9 and nrisinfr a series ofreversals of two different frequencies 'and detecting the. variations inthe operation of the armature of the receiving relay resulting from theeffect of unbalance between the line circuit and its balancing n'etwork. Let it be assumed tliatreversals of a frequency f are beingtransmitted by the transmitter T.l over the line L so as to operate thearmature 7 of the receiving relay h1. When the current from thetransmitter T2 flows through the windings 1 2 and 3 4 yin a definitedirection, it will move the armature 7 to one of its contacts, as forexample, 12. Current will then flow from battery 14 through resistance16 to the junction point of windings 5 6 and through the i'esist-ances10 and 18 and the polar sounder 17 and contact 12 to the opposite sideof the battery. This will charge the condenser 9, located in thevibratory circuit. Furthermore, the-How of current through the winding 6will be in such direction as to create a magneto-motive force which willhave such effect upon the armature 7 as to tend to pull it away from thecontact 12, although itwill not effect the actual opening of thiscontact so long. as the line current from the transmitter T2 `tends toflow in the previously assumed direction through the line windings ofthe relay R1. Vhen the line current through the windings 1 2 and 3 4,falls below va certain minimum value the armature .v7 will move fromcontact 12 and condenser 9 will discharge through a circuit comprisingthe windings 5 and 6 in series with the resistance 10, and the resultantdischarge of current through these windings will be in such direction asto move the armature 7 quickly from contact 12. Since it has beenassumed that the wave being transmitted by the transmitter vT2constitutes 'a series of reversals of frequency f, such as shown incurve 2a, the reversal of the current on the line L and in the windings1 2 and 3 4 will niovethe armature to contact 11 and will cause currentof positive polarity to flow through the vibratory circuit, charging thecondenser 9 in an opposite sense. The How of current through the winding6 will be in a direction as will tend to cause the armature 7 to moveaway from contact 11 and this will be effected by the action of thedischarge of Conde/uscire) tl rough the windings 5 and 6,

as soon as the current in the line windings falls below a definiteminimum amount. The purpose of this vibratory circuit is to overcome thesluggish action of the armature 7 when the current in the line circuitreverses, as in the sending` 'of marking and spacing signals, andprovides therefor a means for obtaining quick positive action of the receiving relay R1. The receipt of a series of reversals of fiiequency fas represented by curve 2a, will cause uniform operation of the armature7. l

lVhile the transmitter T2 is being operatf ed to send over the line Lreversals offrequenc7 f let the transmitter Tl be simultaneouslyoperated for the purpose of transmitting from station X to station Y, aseries of reversals of frequency f. The frequency f may be eitherslightly greater or less than twice the frequency of the signals sentout by the transmitter T1, and will, for illustration, be assumed to beless than 2f. The current from the transmitter T1 will be impressed bythe transmitting circuit 8 across the line L at the junction pointsbetween the windings 1 2 and the windings 3 4, and will` divide, part ofit flowing through the winding l over the line L and back through thewinding t, and the other part flowingthrough the through lthe linebalancing networlrN1 and the winding 3. `Since these ywindings are uponthe ysame core, and since the flow of current is in opposite directionsfrom their respective junction points there will be no resultingmagnetization of thecore if the currents are equal, which shows that theline balancing network exactly "balances electrically the line L. If,however, there exists an unbalance between the line balancing networkand the line circuit then the currents flowing in the windings 1 2 and3&4 from their respective junction points, will be unequal. and theresultant magnetization if large enough will cause a" movement of thearmature 7. The wave shown in curve 2b is the imbalance current thattends to magnetize the core of the re-` lay R1 and thereforeto operatethe armature 7. lt is the difference in the current that flows from themidpoint of the wind ings of R1 through theL line and through the linebalancing network' N1. f This resultant current, due to the inequalityof balance, either adds to or subtracts from the incom-` ing wave offrequency and produces a resultant magnetizing current as shown in curve20. It will be seen that the wave shown in curve 2c vdoes not cross theZero axis at definite intervals of time, but that some of the reversalshave been shortened and others have been lengthened. This distortion ofthe magnetizing current which is produced by the unbalance between theline circuit,l and the balancing network likewinding 2 wise producesirregularity of operation of the armature 7. The armature will notremain upon its contacts for equal periods of time since the time thatit will remain upon any one contact will depend upon the duration of themagnetizing current.

lf there were no unbalance between the network N1 and the line therewould be no unbalance currents flowing in the windings ofthe relay R1and consequently there would be no distortion of the wave of thereceived current represented by curve 2a. Consequently, the armaturemoved between its contacts at a uniform rate which would cause theneedle of the milliami'neter to swing an equal distance from. each sideof the Zero point whenever reversals took place. The imbalance currentwhich results from `imperfect balance be tween the network and the linedistorts the curve of the received current, the resultant to be due tothe introduction of a current of the` frequency shown in the curve 2d'for the particular differences in speed represented by the curves 2auand 2". The armature 7 of they relay, which vibrates at frequency f,willbe biasedv alternately to the marking and the spacing contactslaccording to the rate of change between thereceived reversals of thefrequency f andthe interfering current resulting from the transw mittal.at the rate something less than 2f.l Accordingly, the center ofvibration ofy the milliammeter needle will follow the shifting of thebias, the shift indicating the degree of unbalance. The artificial lineN1 should be` adjusted until the magnitude of the periodio shift is assmall asI it is possible to make it, which indicates the condition. ofbest balance.

In practice the reversals transmitted by vthe circuit 8, connected withthe terminal circuit at station X, should not be much different in speedthan'twice those transmitted at the distant end.,- that is at station Y,so that there will be a slow shifting of the center of vibration of theammeter needle. Tests have shown that a speed of the reversalstransmitted at the distant end should be of the order of from 3 to 6 persecond, and that the phase change between the transmitters at station Yand station X should not be faster than about one cycle per minute forthe best results.

In Fig. l the ammeter has been shown connected in series with thearmature of the relay, but the amineter might be connetted in `serieswith any other local cirr would be T Y 1 thestation Y. If, during theperiod of free vibration, signals are transmitted from the cuit operatedfrom the relay, and the unbalance and distortion might be measuredscribed.

-' Another-method for measuring the' magv'in' a` manner equally as Agood`as that'denitudeof the unb'alancevwhich vdoes not involvetlietransmission of reversals vfrom the e distantstation Yxis as followsrl"he battery vris-removed from the transmitting circuit at theV stationY `and the transmitting branch is closed through an impedance simulatingthe :transmitter T2. The armature ofthe yreceiving relay at station Xwill then vibrateufreely at aperiod determined-by the constants ofthevibratory circuit, which includes the condenser 9, resistance 10 and theinductances of the windings 5 and 6, which are connected in seriestherewith.v This vibratory circuitcoiistitutes in effect avsourcecomparable with the transmitting branch of circuit 8 of station X at aratewhich is `slightly dierent from twice the rate of viv bration of thearmature as'controll'ed by the vibratory circuit, the wave of theresultant current will be similarV to e' thatf shown in lcurve 2c, whichwill produce a shifting-zero ylineas shown in curve 2d. The method ofobtaining the balance is the same as'described heretofore inv connectionwith ther fic;

transmission 'of reversals of frequency "f f from thestation Y. Thismethod provides a speedy method for obtaining the magiiitude oftheunbalance between the network and its line circuit, which method,however,

4is lnot as satisfactory as the one first described in that kthe speedof 'transmission v of reversals from the circuit 8 will .have to .be"adjusted frequently because the vibratingspeedoffthe armature 7 willvary some-A ,r I what.betweeiildifferent termina-l circuits due to thedifferences in their relays, their adv justmentsand other causes.4 Theresults ob- 45.,

tainable should be substantially the same in 'accuracy in' both`methods.

e the invention Although this invention has -been disclosed as embodiedin a definite .form and are f V rangement of parts, it is to beunderstood-` that it is capable of embodiment in other and di'erentforms and arrangements without departing from the spirit and scope of asdefined in the appended claims; f

i ent sourcesallowing the resultant current to control anelectromagnetic device having an indicating device-in series with itsarmature whereby l the degree ofunbalance between the lsaid-networks maybe determined by the ture and its contacts.

variation in the cyclic movement of said armature. 2. The method fordetermining the degree of unbalance lbetween two networks which consistsin impressing a signaling impulse acrosssaid networks, allowing thecurrent resulting from imbalance between said networks to influence theaction of an electromagnetic device tlie armature of which is normallyvibrating at a rate governed by the constants of a circuit with which itis connected and noting by an indicating device connected in series withsaid armature the variation in thezcycli-c movement of the said armatureresulting from the effect of the unbalaiice currents. e

3. The method for determining the degree of imbalance between a linecircuit and its balancing circuit which consists in impressing telegraphsignaling impulses across said circuits in parallel, allowing theresultant current to bias the action 0f an armature vibratingperiodically between its contacts determining the degree of uiibalancebef tween the line circuit and the balancing circuit by the variationinthe cyclic movement of said armature as shown by current indicatingmeans connected between said arma- `4..In a duplex telegraph signalingsystem, the combination `with a line circuit, of an 'artificial line tobe adjusted to balance -the said line circuit,` a relay having certainwindings connecting the said line circuit with the said artificial line,a transmitting circuit bridged across the midpoints of the line windingsof the said relay, a receiving circuit comprising a vibratory circuit,an armature controlled by the said relay having sourcesof ycurrent ofopposite polarity associated therewith, the said armature beingconnected with the said vibratory circuit in such manner as to applythereto impulses of opposite polarity, and an' indicating instrumentconnected between the said armatureand the said vibratory circuit toindicate the distortion of received signals by the transmitted signalsthrough the medium of the armature of said relay.

5. In a duplex telegraph signaling system, the combination with a linecircuit having a source of telegraph signals associated therewith, of anartificial line to balance the said line circuit, a relay havingwindings connecting the said line circuit and the said artificial line,an armature .havingl sources of current of opposite polarity associatedtherewith, a transmitting circuit bridged across the said windingsadapted to apply current reversals to the said line circuit and the saidartificial line in parallel, and a receiving circuit coinprising avibratory circuit having another,

winding of the said relay in series with a condenser and a resistance,the said vibratory circuit being connected through a current measuringdevice with thesaid armature and its associated sources of current insuch manner as to indicate the degree of variation of the cyclicmovement of the said armature resultingi from unbalance between theartificial line and its line circuit.

6. In a duplex telegraph signaling system comprising a line circuit, aplurality of terminal circuits each having a transmitting circuit, areceiving circuit, a balancing network, and a multi-winding relayconnecting the said circuits and the said networks, the method ofmeasuring the magnitude of the imbalance between a line circuit and itsbalancing network at one of the said terminal circuits, which consistsin i111- pressing upon the line circuit at the other of said terminalcircuits current reversals of a definite frequency, simultaneouslyimpressingacross the midpoints of the line windings of the said relay bymeans of the said transmitting circuit current reversals of about twicethe frequency oi the rever sals transmitted from the said terminalcircuit7 allowing the resultant current to operate the armature of thesaid relay whereby impulses of opposite polarity may be impressed uponthe said receiving circuit, the period of operation of the said armaturebeing controlled by the periodic change of the said resultant currentand allowing the said impulses to actuate a current measuring deviceconnecting said receiving circuit whereby the magnitude of the unbalancebetween the said artiicial line and the line circuit may be determined.

In testimony whereof, I have signed my nameto this specification this15th day of July, 1921.

SAMUEL I. CORY.

